Methods for fabricating semiconductor device structures

ABSTRACT

Methods for fabricating semiconductor device structures are disclosed. In some embodiments, methods for fabricating semiconductor device structures may comprising forming at least one raised element on a surface of a substrate, the at least one raised element including sloped sides and a peak, aligning a strip comprising conductive material at least partially over the at least one raised element, and at least partially securing the strip to a surface of the at least one raised element and the surface of the substrate.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No. 11/726,998, filed Mar. 23, 2007, now U.S. Pat. No. 7,759,233, issued Jul. 20, 2010. the disclosure of which is hereby incorporated herein by this reference in its entirety.

FIELD OF THE INVENTION

Embodiments of the present invention relate generally to methods for fabricating strained active-device regions of semiconductor device structures. More specifically, embodiments of the present invention relate to methods in which strips of semiconductor material are applied to a semiconductor substrate in such a way as to stress the semiconductor material of the strips. Embodiments of the present invention also relate to semiconductor device structures with strained active-device regions.

BACKGROUND OF RELATED ART

Improvements in hole mobility have been realized in PMOS devices (i.e., metal-oxide-semiconductor (MOS) devices with n-type, or n-doped, active-device regions and p-type transistor channels), or transistors, by compressively stressing the channels of such devices. Similar improvements in electron mobility have been realized in NMOS devices (i.e., MOS devices with p-type, or p-doped, active-device regions and n-type transistor channels), or transistors, when the channels thereof experience tensile strain.

A number of techniques have been researched to compressively stress PMOS regions, including the inclusion of a strained layer of silicon-germanium (SiGe) within a silicon active-device (e.g., source or drain) region to compressively stress the active-device region, which results in an increase in hole mobility of up to 50%. Strained silicon-germanium layers have also been embedded in the active-device regions of NMOS devices to compressively stress the channels between the active-device regions.

When silicon-germanium is used, a thin layer of silicon-germanium is formed, typically by ultra-high vacuum chemical vapor deposition (CVD) techniques. The layer of silicon-germanium is then capped with a silicon film, which prevents incorporation of germanium into the gate oxide. Lattice mismatches between the silicon-germanium layer and the silicon capping layer generate the desired compressive stress or tensile stress. The silicon-germanium layer may be graded to a relaxed or unstrained state, which generates stress in the silicon capping layer. If both the silicon-germanium layer and the silicon capping layer are thin, they will both be strained. At high gate voltages, the germanium-silicon—silicon capping layer structure has dual-channel characteristics. While many of the carriers or holes are located in the silicon germanium layer, some carriers or holes are also present at the interface between the silicon capping layer and the gate oxide. Unfortunately, the ultra-high vacuum CVD techniques that have been used to fabricate silicon-germanium layers are extremely expensive and, thus, not conducive to use in large-scale semiconductor device fabrication processes.

A number of other experimental techniques for stressing active-device regions of semiconductor device structures have also been developed. Tensile strain has been generated in the channels of NMOS devices by using silicon carbide (SiC) in the active-device regions. Semiconductor device structures have also been bent (which may, e.g., be effected in packaging and encapsulation) to stress the transistor channels. In addition, semiconductor device structures have been fabricated with stress-inducing silicon nitride capping layers.

It would be desirable to develop a process by which transistor channels of semiconductor device structures may be stressed economically and on a scale that is suitable for incorporation into semiconductor device fabrication.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

In the drawings, in which various features of embodiments of the present invention are depicted:

FIGS. 1-9 depict an embodiment of a method according to the present invention for preparing a substrate to induce stress in strips of semiconductor material applied to the substrate;

FIGS. 10 and 11 illustrate a method for forming strips of semiconductor material from a sacrificial substrate;

FIGS. 12-14 show an embodiment of the present invention in which strips of semiconductor material are applied to a substrate and stressed;

FIG. 15 illustrates an embodiment of a semiconductor device structure that includes at least two transistor gates that incorporate strips of strained semiconductor material;

FIG. 16 is a schematic representation of a memory system, according to another embodiment of the present invention, which includes at least one of the types of transistor gates shown in FIG. 15; and

FIG. 17 is a schematic representation of an imaging system, according to yet another embodiment of the present invention that includes at least one of the types of transistor gates shown in FIG. 15.

DETAILED DESCRIPTION

Embodiments of the present invention include applying and securing semiconductor material strips to substrates in such a way as to stress the semiconductor material. As used herein the term “strips” means and encompasses segments of semiconductor material regardless of configuration. Strips of semiconductor material on a given substrate may be compressively stressed, subjected to tensile stress, or some strips may be compressively stressed while other strips are tensilely stressed. Stress may be induced by forming non-planarities on the surface of the substrate to which the strips of semiconductor material are to be secured. The non-planarities may be configured to stress strips of semiconductor material as the strips are secured thereover or to stress strips of semiconductor material as the non-planarities are removed from beneath the strips. The internal strain that ultimately results from stressing the strips of semiconductor material improves carrier mobility (i.e., electron mobility, electron hole pair, or “hole,” mobility) relative to the carrier mobilities of unstrained semiconductor materials.

The edges of the strained semiconductor material strips may be conductively doped with either p-type, or positive charge carrier or hole-generating, dopants, or impurities (e.g., boron (B), aluminum (Al), etc.), or with n-type, or negative charge carrier or electron-donating, dopants, or impurities (e.g., phosphorus (P), arsenic (As), antimony (Sb), etc.). Such conductively doped regions of semiconductor material may, in some embodiments of the present invention, serve as active-device regions (e.g., source and drain regions) of transistors. The central, or middle, regions of the strained semiconductor material strips may serve as the channels for the transistors, such as metal-oxide semiconductor field-effect transistors (MOSFETs). N-channel MOSFETs and P-channel MOSFETs are used together in complementary metal oxide semiconductor (CMOS) devices.

Reference will now be made to the figures wherein like numerals represent like elements. The figures are not necessarily drawn to scale. Elements in the figures are drawn in cross-section.

FIGS. 1-9 depict, in simplified cross-section, an embodiment of a process for forming compression islands 120 a″ (FIG. 9) and tension islands 120 b″ (FIG. 9) on an active surface of a substrate 110. Compression islands 120 a″ and tension islands 120 b″ have dimensions and shapes that are configured to uni-axially or bi-axially stress strips of semiconductor material that will subsequently be applied and secured over the active surface of substrate 110. Compression islands 120 a″ and tension islands 120 b″ may, by way of non-limiting example, be configured as elongate structures that have a collective wave-like appearance on portions of the active surface of substrate 110.

FIG. 1 illustrates a partially fabricated semiconductor device 100. Partially fabricated semiconductor device 100 includes a substrate 110. In some embodiments of the present invention, substrate 110 may be formed from glass, silicon oxycarbide, or aluminum oxycarbide. A non-planarity introducing layer 120 is formed or placed on substrate 110. Non-planarity introducing layer 120 may include an oxidizable semiconductor material, such as silicon (e.g., epitaxial silicon, amorphous silicon, or polycrystalline silicon). Non-planarity introducing layer 120 and substrate 110 together may form a silicon-on-insulator (“SOI”) substrate, such as a silicon-on-glass (“SOG”) substrate, a silicon-on-sapphire (“SOS”) substrate, a silicon-on-ceramic (“SOC”) substrate, silicon on any other suitable insulative material, or another semiconductor material on a compatible and suitable insulative material. In some embodiments, substrate 110 may include an SOG substrate in which the glass is borosilicate glass (“BSG”) (e.g., PYREX®), fused silica, fused quartz, silicon oxycarbide, aluminum oxycarbide. U.S. Patent Application Publication 2004/0232487, published Nov. 25, 2004; U.S. Patent Application Publication 2005/0167752, published Aug. 4, 2005; U.S. Patent Application Publication 2005/0020094, published Jan. 27, 2005; and U.S. Pat. No. 7,008,854, issued Mar. 7, 2006; the disclosure of each of which is hereby incorporated herein in their entireties by this reference, disclose different types of glass from which substrate 110 may be formed. Substrate 110 may, commensurate with known semiconductor device fabrication techniques, comprise a wafer or other bulk substrate upon which a large plurality of semiconductor devices 100 are simultaneously fabricated.

In embodiments of the present invention, non-planarity introducing layer 120 will be formed (e.g., deposited, laminated, formed in situ or otherwise formed) by known processes and modified to form oxide islands on the surface of substrate 110. The oxide islands function as non-planarities that are used to apply stress to semiconductor material strips secured thereover or therebetween. In one embodiment, the oxide islands are formed by removing material from select regions of non-planarity introducing layer 120. An oxide is formed over non-planarity introducing layer 120 and then subsequently planarized. Non-planarity introducing layer 120 is then oxidized to form hills and valleys across the surface of substrate 110. Material is then uniformly removed from non-planarity introducing layer 120 until substrate 110 is exposed. Thus, the oxide hills become oxide islands on the surface of substrate 110.

Mask 130 as illustrated in FIG. 2 may be used to govern the removal of material from non-planarity introducing layer 120. Mask 130 may be formed on non-planarity introducing layer 120 and may comprise any suitable resist material known in the art. In some embodiments, mask 130 may include a photoresist, such as a conventional photoresist that is configured to at least partially cross-link when exposed to electromagnetic radiation having a wavelength of 248 nm or 193 nm. Mask 130 may also be formed from a material that at least partially cross-links when exposed to an electron beam or X-rays. In other embodiments, mask 130 may include a carbon-based mask (e.g., transparent carbon, etc.). In still other embodiments, mask 130 may be a hard mask (e.g., formed from silicon nitride, silicon oxynitride, etc.). Mask 130 may include multiple layers of different materials. Mask 130 may be formed by methods known to those of ordinary skill in the art. FIG. 3 illustrates a patterned mask 130 that includes protective regions 130 a and apertures or other open areas 135 formed in between protective regions 130 a.

FIG. 4 illustrates non-planarity introducing layer 120 after material has been removed (e.g., with a suitable etchant) from regions exposed through apertures 135 of mask 130. The removal of material from non-planarity introducing layer 120 may be accomplished by an etch process, such as a dry etch selective for the non-planarity introducing layer 120 over the protective regions 130 a of mask 130. The removal of such material from non-planarity introducing layer 120 results in the formation of isolation trenches 122 and tension trenches 124 in non-planarity introducing layer 120. Compression hills 120 a are located between isolation trenches 122. Tension trenches 124 are located between tension hills 120 b. Compression hills 120 a and tension hills 120 b are formed from regions of non-planarity introducing layer 120 shielded by protective regions 130 a of mask 130 during the material removal process. Compression hills 120 a and tension hills 120 b will be used to form oxide islands on the surface of substrate 110. The depths of isolation trenches 122 and tension trenches 124 may be selected to provide non-planarities of desired dimensions and shapes on the surface of substrate 110 once the trenches 122, 124 are filled with an oxide and non-planarity introducing layer 120 is subsequently oxidized. After oxidation, the heights of compression hills 120 a and tension hills 120 b are greater than the thicknesses of the regions that were previously filled with oxide.

FIG. 4 also depicts a first transistor region 300 and a second transistor region 350. Transistors will eventually be formed in first transistor regions 300 and second transistor regions 350. Commensurate with conventional semiconductor device fabrication practices, partially fabricated semiconductor device 100 may include numerous transistor regions. As illustrated, isolation trenches 122 may separate first transistor regions 300 and second transistor regions 350. Within first transistor regions 300 are compression regions 320. Compression regions 320 serve to illustrate the regions where compressive strain will eventually be introduced into semiconductor material strips. The top of each compression hill 120 a defines the center of each compression region 320. Within second transistor regions 350 are tension regions 370. Tension regions 370 serve to illustrate the regions where tensile strain will eventually be introduced into semiconductor material strips applied to substrate 110. The tops of each pair of tension hills 120 b define the boundaries of tension regions 370. The center of each tension trench 124 defines the center of each tension region 370.

After material is removed from non-planarity introducing layer 120, protective regions 130 a of mask 130 may be removed as illustrated in FIG. 5. Protective regions 130 a may be removed by any method known in the art, such as with a strip for a photomask or an etch for a hard mask. In embodiments where protective regions 130 a include transparent carbon, an etch utilizing nitrogen, oxygen, and bromic acid may be used to remove solid protective regions 130 a.

FIG. 6 depicts blanket layer 140 formed over non-planarity introducing layer 120 and filling isolation trenches 122 and tension trenches 124. Blanket layer 140 may be formed before or after solid protective regions 130 a are removed. Blanket layer 140 may be formed by any method known in the art, such as atomic layer deposition (ALD) processes or chemical vapor deposition (CVD) processes.

Blanket layer 140 may comprise the same material as, or a similar material to, the material of an oxide of non-planarity introducing layer 120 to be subsequently formed (i.e., similar to the oxide that will result from the oxidation of non-planarity introducing layer 120). Blanket layer 140 may include an oxide or any other material that is removable (e.g., by etching) at a similar rate and under the same conditions as an oxide of non-planarity introducing layer 120. In embodiments where non-planarity introducing layer 120 includes silicon as the material to be oxidized, blanket layer 140 may include silicon oxides or any other material that is removable at a rate similar to the removal rate of the silicon oxides.

After blanket layer 140 is formed, blanket layer 140 is planarized, as depicted in FIG. 7. Blanket layer 140 may be planarized by any suitable method known in the art. In some embodiments, known abrasive planarization techniques such as chemical-mechanical planarization (CMP) processes may be used. Blanket layer 140 is planarized until the tops of compression hills 120 a and tension hills 120 b are substantially coplanar with the remaining portions of blanket layer 140 filling isolation trenches 122 and tension trenches 124 (i.e., planarized blanket layer portions 140 a and 140 b).

After planarization of blanket layer 140, which exposes compression hills 120 a and tension hills 120 b, non-planarity introducing layer 120 is oxidized, as illustrated in FIG. 8. The oxidation of non-planarity introducing layer 120 may be accomplished by any suitable method known in the art, such as by thermal oxidation. The oxidation of non-planarity introducing layer 120 results in different oxide thicknesses (i.e., non-planarities) on different regions of the surface of substrate 110. Exposed compression hills 120 a and tension hills 120 b oxidize more rapidly than regions covered by planarized blanket layer portions 140 a and 140 b. Oxidized compression hills 120 a′ and oxidized tension hills 120 b′ are increased in thickness by the oxidation. Sloped blanket layers 140 a′ and 140 b′ are sloped by the formation of slowly tapering oxide wedges, which are referred to as “bird's beaks,” which are formed by the lateral diffusion of oxidants under the edges of planarized blanket layer portions 140 a and 140 b. The bird's beak has a shape similar to that formed during a LOCal Oxidation of Silicon (“LOCOS”) process. LOCOS processes and oxidation processes are known in the art, and include without limitation those disclosed in U.S. Patent Application Publication 2004/0173798, published Sep. 9, 2004, and U.S. patent application Ser. No. 11/498,586, filed Aug. 3, 2006, the disclosure of each of which document is hereby incorporated herein in its entirety by this reference.

Next, material is removed from oxidized non-planarity introducing layer 120′, such as with a known etch process (e.g., an anisotropic etch), to expose the surface of substrate 110. Sloped blanket layers 140 a′ and 140 b′ may be substantially entirely removed, as depicted in FIG. 9, to form isolation valleys 122 a and tension valleys 124 a, respectively. The bird's beaks remain at the edges of oxidized compression hills 120 a′ and tension hills 120 b′, which remain on the surface of substrate 110 in the form of compression islands 120 a″ and tension islands 120 b″.

In some embodiments, the dimensions of compression islands 120 a″ and tension islands 120 b″ may be tailored to apply a desired type and/or amount of stress to strips 250 a′ and 250 b′ of semiconductor material applied thereover (FIGS. 11 and 12). The semiconductor material of strips 250 a′ and 250 b′ and the results of stressing that semiconductor material may determine how much strain will ultimately occur in the semiconductor material. It may be desirable to stress the semiconductor material strips 250 a′ and 250 b′ such that their lengths are compressed or stressed, respectively, by as much as about 0.5% or more. The lengths of the semiconductor material strips 250 a′, 250 b′ may be compressed or stretched about 0.75% to about 1.5%. A stress range of about 1% to about 1.2% may be targeted during fabrication to avoid altering the lengths of the semiconductor material strips 250 a′, 250 b′ by less than about 0.75% or more than about 1.5%.

The dimensions and shapes of compression islands 120 a″ and/or tension islands 120 b″ may, in embodiments of the present invention, be tailored to act in conjunction with the respective crystal orientations of the semiconductor material of strips 250 a′, 250 b′ to stress the semiconductor material strips 250 a′, 250 b′ in the desired manner and to the desired extent. In this regard, strained semiconductor material strips 250 a′, 250 b′ may, in various embodiments, include mono-crystalline semiconductor material. The mono-crystalline semiconductor material may be oriented in a number of different possible planes relative to surfaces of the strip formed from the mono-crystalline semiconductor material. The different “surface orientations,” which are referred to herein using conventional Miller indices in parentheses, include (100), (110), and (111) surface orientations. Relative to a given surface orientation, some directions within a crystal structure may exhibit more carrier mobility than others (i.e., some directions are more conductive than others). Different directions are identified herein using angle brackets (e.g., <100>, <110>, etc.).

With reference now to FIGS. 10-14, an embodiment of a method for forming strips of semiconductor material, securing the same in place over the active surface of substrate 110, and inducing stress in the strips of semiconductor material is illustrated.

FIG. 10 illustrates a sacrificial substrate 200, such as a semiconductor wafer (e.g., a mono-crystalline silicon wafer or any other material with conductive properties that may be altered when strained). Sacrificial substrate 200 may include silicon, germanium, silicon-germanium, gallium arsenide, indium phosphide, or any other suitable semiconductor material. Sacrificial substrate 200 has a selected crystal orientation (e.g., a (100), (110), or (111) orientation).

Unremoved strips 250 are formed in sacrificial substrate 200 so as to enable their mobility directions to be oriented or stressed (and ultimately strained) in a desired manner. Tensile strain in a <110> channel direction (i.e., desired direction of mobility of a silicon surface serving as a channel in a transistor) optimizes electron mobility in a (100) surface orientation semiconductor material, while compressive strain in a <110> channel direction optimizes hole mobility in a (100) surface orientation semiconductor material. Hole mobility may also be optimized in semiconductor material with a (110) surface orientation when tensile strain is present in the <100> direction.

Unremoved strips 250 are defined in a surface of sacrificial substrate 200 by known processes, such as the so-called “smart-cut” technology disclosed in U.S. Patent Application Publication 2004/0224480, published Nov. 11, 2004, the entire disclosure of which is hereby incorporated herein by this reference. In embodiments where “smart-cut” technology is utilized, hydrogen species, such as H⁺, H₂ ⁺, D⁺, or D₂ ⁺ ions (where “D” represents deuterium), may be used as implantation species 240. The dimensions (e.g., the width, length, and thickness) of unremoved strips 250 are controlled by the peripheral boundaries of horizontal implantation locations and the implantation depth of implantation species 240 implanted in sacrificial substrate 200.

Implantation species 240 are implanted along back side plane 210 as illustrated in FIG. 10, which will eventually define the back side of unremoved strips 250. The depth of back side plane 210 will determine the thickness of unremoved strips 250. The thicknesses of unremoved strips 250 may be sufficient to generate a desired amount of strain in the semiconductor material of the unremoved strips 250. Unremoved strips 250 may have thicknesses of about 1000 Å or less, of about 300 Å or less, of about 100 Å or less, or of about 50 Å or less.

Implantation species 240 are also implanted along edge planes 220 to define the peripheries (e.g., ends and sides) of unremoved strips 250. The widths of unremoved strips 250 may be narrow relative to the lengths of the strips. Without limiting the scope of the present invention, unremoved strips 250 may have widths of about 300 Å to about 1000 Å.

Contact faces 230 of unremoved strips 250, which are the surfaces of unremoved strips 250 that are exposed on the surface of sacrificial substrate 200 prior to removing unremoved strips 250 therefrom, will be the surfaces used to contact the oxide islands 120 a″, 120 b″ protruding from the surface of substrate 110, as well as the surface of substrate 110, as shown in FIG. 11. A native oxide (not shown) may or may not be present (i.e., the native oxide may be removed or prevented from forming) on each contact face 230. If a native oxide is present, the native oxide may be formed either before or after implantation with implantation species 240.

After implantation, as depicted in FIG. 11, sacrificial substrate 200 may be oriented relative to a fabrication substrate 110 such that strips 250 a and 250 b are aligned over corresponding islands 120 a″, 120 b″ and such that the crystal orientation of the semiconductor material of strips 250 a, 250 b is parallel to the desired direction of carrier mobility (i.e., electron mobility or hole mobility). Contact faces 230 a of strips 250 a may be positioned over, brought into contact with, and secured to the peaks of compression islands 120 a″. A contact face 230 b of each strip 250 b is positioned over, brought into contact with, and secured over a tension valley 124 a, secured to the peaks of a pair of tension islands 120 b″ located on either side of tension valley 124 a proximate ends thereof defined by edge planes 220. In some embodiments, strips 250 a and 250 b may be initially secured to the peaks of their respective islands 120 a″, 120 b″ by van der Waals forces.

After initially securing unremoved strips 250 a and 250 b to the peaks of their respective islands 120 a″, 120 b″, unremoved strips 250 a and 250 b are separated from sacrificial substrate 200. Heat and/or mechanical stress (e.g., bending, torsion, etc.) may be utilized to disengage, or break the back sides 210 and edges of strips 250 a and 250 b free from the remainder of sacrificial substrate 200 and, thus, to remove the strips 250 a and 250 b from the remainder of sacrificial substrate 200.

Heat may also be used to strengthen the respective bonds between strips 250 a and 250 b and the peaks of islands 120 a″ and 120 b″. In one embodiment, the bond is strengthened at a temperature between about 300° C. and 400° C. The same heating process used to separate unremoved strips 250 a and 250 b from sacrificial substrate 200 may be used to strengthen the respective bonds between the unremoved strips 250 a and 250 b and the respective peaks of islands 120 a″ and 120 b″.

FIG. 11 illustrates the simultaneous removal of strips 250 a and 250 b from a sacrificial substrate 200, as well as their simultaneous application to a fabrication substrate 110, which is useful when strips 250 a″ and 250 b″ (FIGS. 13 and 14) having the same crystal orientations with strain in parallel carrier mobility directions are desired. In one embodiment, semiconductor material strips 250 a and 250 b with a (100) surface orientation may be oriented over substrate 110 so as to be subsequently strained (strips 250 a will ultimately be compressively strained, while strips 250 b will ultimately be tensilely strained) in the <110> direction. In another embodiment, semiconductor material strips 250 a and 250 b with a (111) surface orientation may be oriented over substrate 110 so as to be subsequently respectively, compressively and tensilely strained in the <110> direction.

However, in embodiments where strips 250 a, 250 b with different crystal orientations or strips 250 a, 250 b having different carrier mobility directions are to be applied to a single substrate, a first set of strips 250 a, 250 b may be provided by a sacrificial substrate 200 and secured to substrate 110 separately from a second set of strips 250 a, 250 b, which are separately provided from the same sacrificial substrate 200 or a different sacrificial substrate 200. In such embodiments, strips 250 a and 250 b may be secured to their respective islands 120 a″ and 120 b″ of a fabrication substrate 110 in separate process acts. In one such embodiment, strips 250 a may have a (100) surface orientation and be oriented so as to subsequently be compressively strained in the <110> direction, while strips 250 b may have a (110) surface orientation and be oriented so as to subsequently be tensilely strained in the <100> direction.

After removal from sacrificial substrate 200, semiconductor material strips 250 a′ and 250 b′ are further secured to the peaks of the islands 120 a″, 120 b″, as depicted in FIG. 12. In some embodiments and as previously mentioned, van der Waals forces are sufficient to influence the conformation of semiconductor material strips 250 a′ and 250 b′ to substrate 110 and the previously uncontacted portions of each of the islands 120 a″, 120 b″. In such embodiments, upon their separation from sacrificial substrate 200, semiconductor material strips 250 a′ and 250 b′ automatically conform to the topography of substrate 110, islands 120 a″ and 120 b″ and tension valleys 124 a, as depicted in FIG. 13.

In other embodiments, one or both of the semiconductor material strips 250 a′ and 250 b′ do not automatically conform to the shapes of their corresponding islands 120 a″ and 120 b″ and into tension valleys 124 a, such as is depicted in FIG. 13. In such embodiments, known techniques, such as nano-scale imprint mask technology, may be used to influence the conformance of the semiconductor material strips 250 a′ and/or 250 b′. A nano-scale imprint mask (not shown), which acts as a press, can be made with very small raised areas that are located and configured to force elevated regions of the semiconductor material strips 250 a′, 250 b′ into the tension valleys 124 a or recesses over which they are elevated. Other techniques employing heat and pressure may also be used to influence conformance of semiconductor material strips 250 a′ and 250 b′ to the shapes of their corresponding islands 120 a″, 120 b″ and, where desired, intervening valleys such as tension valleys 124 a. In one embodiment, semiconductor material strips 250 a′ and 250 b′ may be separated from sacrificial substrate 200 in a vacuum and then atmospheric pressure may be applied to influence conformance of semiconductor material strips 250 a′ and 250 b′.

Notably, the conformance of semiconductor material strips 250 a″, as depicted in FIG. 13, may apply little or no stress to the semiconductor material strips 250 a″, as the ends of the semiconductor material strips 250 a″ may be free to move during conformance.

The conformance of semiconductor material strips 250 b″ may introduce tensile stress TS into the semiconductor material strips 250 b″, as depicted in FIG. 13. The ends of each of the semiconductor material strips 250 b″ respectively secured to peaks of a pair of tension islands 120 b″ and so remain stationary as the center of each semiconductor material strip 250 b″ is drawn or forced into conformance with remaining portions of the pair of tension islands 120 b″ and tension valley 124 a therebetween. Van der Waals forces initially secure semiconductor material strips 250 a″ and 250 b″ to the islands 120 a″, 120 b″ and to adjacent regions of the exposed surface of substrate 110. The semiconductor material strips 250 a″, 250 b″ may be further secured to their respective islands 120 a″, 120 b″ and/or substrate 110 with heat (e.g., a temperature of about 300° C. to about 400° C.). As a resulting internal tensile strain will ultimately be present in the semiconductor material of strips 250 b″ of this embodiment, they are also referred to herein as “strained semiconductor material strips 250 b″,” or more simply as “strips 250 b″.”

With reference now to FIG. 14, in embodiments where strips 250 a′ and 250 b″ (FIGS. 12 and 13) have been secured in place over substrate 110, strips 250 b″ may be masked (e.g., with a mask 255 of any suitable type, as shown) to prevent removal of their corresponding tension islands 120 b″. Compression islands 120 a″, which underlie strips 250 a′ and are exposed through apertures or other open areas in mask 255, may be removed. Undercutting etch processes, such as isotropic wet or dry etches, may be used to remove compression islands 120 a″ from beneath strips 250 a′. The etchant that is employed may remove the material of the compression islands 120 a″ with selectivity over the semiconductor material of strips 250 a′ and the material or materials of substrate 110. In a specific embodiment where strips 250 a′ include silicon and compression islands 120 a″ include silicon dioxide, a wet etchant including hydrofluoric acid may be used. In another specific embodiment where strips 250 a′ include silicon and compression islands 120 a″ include silicon dioxide, a plasma etch including species derived from CH₄, O₂, and H₂ may be used to remove silicon dioxide with selectivity over silicon.

After compression islands 120 a″ are removed, semiconductor material strips 250 a′, 250 a″ (FIGS. 12 and 13) conform to substrate 110 as illustrated in FIG. 14. As compression islands 120 a″ are removed, the fixed edge portions of strips 250 a″ remain stationary as the center of each strip 250 a″ is drawn (e.g., by van der Waals forces) and/or forced into contact with the active surface of substrate 110 by previously mentioned techniques, which introduces compressive stress CS in strips 250 a″. As a result, internal compressive strain will ultimately be present in the semiconductor material of strips 250 a″ of this embodiment, they are also referred to herein as “strained semiconductor material strips 250 a″,” or more simply as “strips 250 a″.”

Exposed surfaces of strips 250 a′, 250 a″, 250 b″ may, in some embodiments, be polished to reduce the thickness thereof. Polishing may be accomplished by any method known in the art, such as by chemical polishing and CMP processes.

Strained semiconductor material strips 250 a″ and 250 b″ may be further bonded to substrate 110. Heat may be used to strengthen the bond between the strained semiconductor material strips 250 a″ and 250 b″ and substrate 110. In one embodiment, the bond is strengthened at a temperature between about 800° C. and about 1000° C. In some embodiments, after strained semiconductor material strips 250 a″ and 250 b″ are further bonded to substrate 110, grinding, polishing, chemical etch, or plasma etch may be used to further thin strained semiconductor material strips 250 a″ and 250 b″.

FIGS. 1-14 illustrate embodiments for forming, placing, and applying stress to semiconductor material strips 250 a′ and 250 b′ to form strained semiconductor material strips 250 a″ and 250 b″ on substrate 110. FIG. 14 illustrates a compressively strained semiconductor material strip 250 a″ adjacent a tensilely strained semiconductor material strip 250 b″. Alternatively, embodiments of the process depicted in FIGS. 1-14 may be modified by suitable placement of oxide islands 120 a″, 120 b″ to form strained semiconductor material strips 250 a″ adjacent other strained semiconductor material strips 250 a″ and/or strained semiconductor material strips 250 b″ formed adjacent other strained semiconductor material strips 250 b″.

Semiconductor device structures incorporating strained semiconductor materials strips 250 a″ and 250 b″ are illustrated in FIG. 15. In particular embodiments, transistors, such as MOSFETs, may be formed using the strips. Each transistor may include, among numerous other contemplated elements, a source, a drain, a channel, a gate dielectric, a gate, and sidewall spacers, as described in further detail hereinafter. A strained semiconductor material strip 250 a″, 250 b″ may serve as the source, drain, and channel for each transistor.

FIG. 15 depicts a semiconductor device structure 100 according to embodiments of the present invention that includes a first transistor region 300′ and a second transistor region 350′ that include strained semiconductor material strips 250 a″ and 250 b″, respectively. The transistor components illustrated may be modified, deleted, or added to as desired. Gate dielectrics 301, 301′ are depicted as formed on the top and sides of strained semiconductor materials strips 250 a″ and 250 b″. Gate dielectrics 301, 301′ may serve to isolate transistors formed in first transistor regions 300′ from transistors formed in second transistor regions 350′. Gates 302, 302′ may be formed on gate dielectrics 301, 301′. Lightly doped regions 303, 303′ may be shallowly formed in the ends of strained semiconductor material strips 250 a″ and 250 b″. Sidewall spacers 304, 304′ may be formed on gate dielectrics 301, 301′ and adjacent gates 302, 302′. Active device regions 305, 305′ may also be formed, as known in the art. Active device regions 305, 305′ and lightly doped regions 303, 303′, which will serve as the source and drain for each of the transistors, may be formed by known dopant implantation processes or otherwise, as known in the art. Active device regions 305, 305′ and lightly doped regions 303, 303′ may be doped with an n-type dopant, or impurity, to form n-type regions, or with a p-type dopant, or impurity, to form p-type regions. Sidewall spacers 304, 304′ may serve to minimize the amount of active device regions 305, 305′, which extend beneath gates 302, 302′ and thereby reduce parasitic capacitance. The central, or middle region of each of the strained semiconductor material strips 250 a″ and 250 b″, which is strained, may serve as the channel 306, 306′ for its corresponding transistor regions 300′, 350′. Methods of forming gate dielectrics 301, 301′, gates 302, 302′, and sidewall spacers 304, 304′ are well known in the art. Thus, transistors may be formed in the transistor regions 300′, 350′, each transistor having a source, drain, and channel with improved mobility.

The numerous possible detailed processing acts of forming transistors are known in the art and have not been discussed herein. Specifically, methods of forming transistors, such as P-channel MOSFETs, N-channel MOSFETs, and CMOS devices, are known in the art and may be used with strained semiconductor materials strips 250 a″ and 250 b″. U.S. Pat. No. 6,255,698, issued Jul. 3, 2001, the disclosure of which is hereby incorporated herein in its entirety by this reference, discloses embodiments of CMOS fabrication processes that may be used to fabricate transistor regions 300′, 350′ of a semiconductor device structure.

FIG. 15 depicts only one embodiment of a semiconductor device structure 100 and transistor regions 300′, 350′ thereof that may be formed using strained semiconductor material strips 250 a″ and 250 b″. First transistor regions 300′ may include strained P-channel MOSFETs having improved hole mobility due to compressive strain therein. Second transistor regions 350′ may include strained N-channel MOSFETs with improved electron mobility or strained P-channel MOSFETs with improved hole mobility, each due to tensile strain therein.

FIG. 15 depicts a first transistor region 300′ adjacent to a second transistor region 350′. Such an arrangement may be useful when fabricating P-channel MOSFETs adjacent to N-channel MOSFETs, such as in a CMOS design. In other embodiments, first transistor regions 300′ may be formed adjacent other first transistor regions 300′. This may be desirable when fabricating primarily P-channel MOSFETs. In still other embodiments, second transistor regions 350′ may be formed adjacent to other second transistor regions 350′. This may be desirable when fabricating primarily N-channel MOSFETs.

In other embodiments, transistor regions 350′ may be formed to adjacent other transistor regions 350′, with some of the transistor regions 350′ comprising P-channel MOSFETs with strips 250 b″ being strained in a first direction and others of the transistor regions 350′ being N-channel MOSFETs that include strips 250 b″ that are strained in a second direction. More specifically, one set of transistor regions 350′ may include strips 250 b″ having a (100) or (111) surface orientation that are under tensile strain in the <110> direction, while another set of transistor regions 350′ include strips 250 b″ with a (110) surface orientation under tensile strain in the <100> direction.

Embodiments of the present invention also include systems including devices comprising structures formed with strained semiconductor material. The memory system 400 depicted in FIG. 16 and imaging system 500 depicted in FIG. 17 are two embodiments of such systems.

A memory system 400 may include a memory 410 in communication with a processor 420 as depicted in FIG. 16. Memory system 400 may also include input/output devices 430 in communication with processor 420. Both memory 410 and processor 420 may include numerous transistors 401 according to embodiments of the present invention. Transistors 401 include strained semiconductor material strips 250 a″ and/or 250 b″ according to embodiments of the present invention. Additionally, input/output devices 430 may also include transistors 401 with strained semiconductor material strips 250 a″ and/or 250 b″. Memory system 400 may include additional components not depicted, as is known in the art. Memory system 400 may be part of a larger system. Embodiments of such larger systems include, without limitation: computer systems, information handling systems, telecommunications systems, camera systems, video recording and playing systems, television systems, computer display systems, game systems, phone systems, wireless systems, automobile systems, aircraft systems, industrial control systems, and others.

Memory 410 may include one or more types of memory circuits, and various combinations thereof. Possible embodiments of memory 410 in which embodiments of strained semiconductor material strips 250 a″, 250 b″ of the present invention may be used include, but are not limited to, Dynamic Random Access Memory (“DRAM”), Static Random Access Memory (“SRAM”), PseudoStatic Random Access Memory, (“PSRAM”), and Flash Memories. DRAM includes, without limitation, synchronous DRAM (SDRAM), SDRAM II, Double Data Rate DRAM (“DDR DRAM”), DDR2 DRAM, and DDR3 DRAM. Flash Memory includes, but is not limited to, NAND (i.e., boolean “Not AND”) Flash and NOR (i.e., boolean “Not OR”) Flash. Processor 420 may be any processor known in the art. Input/output devices 430 may be any input/output devices known in the art.

FIG. 17 illustrates an imaging system 500 according to an embodiment of the present invention. Imaging system 500 includes a CMOS imager 510 and processor 520. CMOS imager 510 includes a pixel array 511, timing and control circuitry 512, a row address decoder 513, a row driver 514, a column driver 515, and a column address decoder 516. Each pixel of pixel array 511 may include transistors 501. Transistors 501 include strained semiconductor material strips 250 a″ and/or 250 b″ according to embodiments of the present invention. The pixels of pixel array 511 are arranged in rows and columns. Rows are activated by row driver 514 in response to row address decoder 513. Columns are activated by column driver 515 in response to column address decoder 516. Timing and control circuitry 512 control row address decoder 513 and column address decoder 516. CMOS imager 510 may include other components as is known in the art. Processor 520 communicates with CMOS imager 510, as known in the art.

Imaging system 500 may be part of larger system, such as a computer system, camera system, scanner system, machine vision system, vehicle navigation system, video phone system, surveillance system, auto focus system, star tracker system, motion detection system, image stabilization system, data compression system, such as for high-definition television, and others. Additionally, memory system 400 and imaging system 500 may be subcomponents of a common, larger system.

The foregoing embodiments should not be considered to limit the scope of semiconductor device structures in which strained semiconductor material strips 250 a″, 250 b″ according to embodiments of the present invention may be used.

Although this invention has been described with reference to particular embodiments, the invention is not limited to these described embodiments. Rather, the invention is limited only by the appended claims, which include within their scope all equivalent methods, processes, devices, and systems that operate according to the principles of the invention as described. 

1. A method for fabricating a semiconductor device structure, comprising: forming at least one raised element on a surface of a substrate, the at least one raised element including sloped sides and a peak; aligning a strip comprising conductive material at least partially over the at least one raised element wherein aligning the strip comprises positioning a sacrificial substrate in which the strip has been formed over the semiconductor substrate; bringing the strip into contact with at least one corresponding raised element; removing the strip from the sacrificial substrate while removing the sacrificial substrate from the semiconductor substrate; and at least partially securing the strip to a surface of the at least one raised element and the surface of the substrate.
 2. The method of claim 1, wherein aligning the strip comprises aligning a central portion of a length of the strip over the peak of the at least one raised element and at least partially securing the strip comprises securing the strip over the at least one raised element and to the surface of the substrate on opposing sides thereof.
 3. The method of claim 2, further comprising: removing material of the at least one raised element from beneath the strip with opposing ends of the strip remaining secured to the substrate surface.
 4. The method of claim 3, further comprising providing the strip having a (100) surface orientation to subject the strip to compressive stress in a <110>direction by removing the material of the at least one raised element from beneath the strip.
 5. The method of claim 3, further comprising providing the strip having a (111) surface orientation to subject the strip to compressive stress in a <110>direction by removing the material of the at least one raised element from beneath the strip.
 6. The method of claim 1, wherein forming the at least one raised element comprises forming adjacent raised elements, and further comprising: aligning a central portion of a length of the strip over a valley between the adjacent raised elements, with each end of the strip being positioned over one of the adjacent raised elements and at least partially securing the strip comprises securing each end of the strip to a raised element.
 7. The method of claim 6, further comprising forcing the strip against the surface of the substrate between the adjacent raised elements.
 8. The method of claim 7, further comprising providing the strip having a (100) surface orientation to subject the strip to tensile stress in a <110> direction by forcing the strip against the surface of the substrate between the adjacent raised elements.
 9. The method of claim 7, further comprising providing the strip having a (110) surface orientation to subject the strip to tensile stress in a <100> direction by forcing the strip against the surface of the substrate between the adjacent raised elements.
 10. The method of claim 7, further comprising providing the strip having a (111) surface orientation to subject the strip to tensile stress in a <110> direction by forcing the strip against the surface of the substrate between the adjacent raised elements.
 11. The method of claim 1, wherein forming the at least one raised element comprises: forming a layer of semiconductor material on a surface of a substrate; removing semiconductor material from regions of the layer to form recesses therein; introducing an oxide into the recesses; planarizing the oxide so a surface of each oxide structure is substantially coplanar with a surface of remaining portions of the layer; oxidizing the semiconductor material of remaining portions of the layer to form a resulting oxide structure including raised elements where semiconductor material was previously exposed; and removing the oxide to expose the substrate laterally beyond the raised elements.
 12. The method of claim 1, wherein removing the strip comprises exposing at least the sacrificial substrate to heat.
 13. The method of claim 1, wherein removing the strip comprises applying mechanical stress to at least the sacrificial substrate.
 14. The method of claim 1, wherein at least partially securing the strip comprises heating at least the strip.
 15. The method of claim 1, further comprising: polishing an exposed surface of the strip after at least partially securing the at least one strip. 